Aranda A, Pérez-Ortín J E, Moore C, del Olmo M L
Departament de Bioquímica i Biologia Molecular, Facultats de Ciències, Universitat de València, Spain.
RNA. 1998 Mar;4(3):303-18.
Efficient transcription termination downstream of poly(A) sites has been shown to correlate with the strength of an upstream polyadenylation signal and the presence of a polymerase pause site. To further investigate the mechanism linking termination with 3'-end processing, we analyzed the cis-acting elements that contribute to these events in the Saccharomyces cerevisiae FBP1 gene. FBP1 has a complex polyadenylation signal, and at least three efficiency elements must be present for efficient processing. However, not all combinations of these elements are equally effective. This gene also shows a novel organization of sequence elements. A strong positioning element is located upstream, rather than downstream, of the efficiency elements, and functions to select the cleavage site in vitro and in vivo. Transcription run-on analysis indicated that termination occurs within 61 nt past the poly(A) site. Deletion of two UAUAUA-type efficiency elements greatly reduces polyadenylation in vivo and in vitro, but transcription termination is still efficient, implying that FBP1 termination signals may be distinct from those for polyadenylation. Alternatively, assembly of a partial, but nonfunctional, polyadenylation complex on the nascent transcript may be sufficient to cause termination.
聚腺苷酸化位点下游的高效转录终止已被证明与上游聚腺苷酸化信号的强度以及聚合酶暂停位点的存在相关。为了进一步研究将终止与3'端加工联系起来的机制，我们分析了酿酒酵母FBP1基因中促成这些事件的顺式作用元件。FBP1具有复杂的聚腺苷酸化信号，并且为了进行高效加工必须存在至少三个效率元件。然而，这些元件的并非所有组合都同样有效。该基因还显示出序列元件的一种新颖组织方式。一个强定位元件位于效率元件的上游而非下游，并且在体外和体内都起到选择切割位点的作用。转录延伸分析表明终止发生在聚腺苷酸化位点下游61个核苷酸内。缺失两个UAUAUA型效率元件会在体内和体外极大地降低聚腺苷酸化，但转录终止仍然高效，这意味着FBP1终止信号可能与聚腺苷酸化的终止信号不同。或者，在新生转录本上组装一个部分但无功能的聚腺苷酸化复合物可能足以导致终止。
